1. Field of the Invention
The present invention relates to an image reading apparatus for reading image information of originals, for example, an image reading apparatus, such as an image scanner or a facsimile apparatus. The present invention also relates to an image forming apparatus, such as a copying machine, in which the image reading apparatus is mounted.
2. Related Background Art
Conventionally, as copying machines, composite machines having a copying function and a facsimile function, and image scanners having an auto document feeder (hereinafter referred to as ADF), there have been proposed a number of apparatuses having both the function by which scanning is performed with the original remaining stationary on a glass sheet surface and the function (flow reading function) by which scanning is performed while moving the original with the optical system being stationary.
Regarding the construction of the portion in which the flow reading of originals is performed, various proposals have been made in connection with the ensuring of the reading position, the conveying of originals, etc.
For example, Japanese Patent Publication (Kokoku) No. 3-37348 proposes a construction in which an ADF is secured to the apparatus main body, with the ADF being separated from an original pressure plate, and in which the height of the reading position using the original glass stand is made the same as the height of the position at which the original fed by the ADF is read.
Further, Japanese Utility Model Publication (Kokoku) No. 5-43561 discloses a construction in which there is provided a presser member for defining a fixed gap between a contact-type image sensor (hereinafter referred to as CIS) and an original pressure roller opposed thereto to ensure a focal distance.
Further, Japanese Patent application Laid-Open (Kokai) No. 63-138863 discloses a construction in which a U-turn-conveyed original is read, and then conveyed in a discharge direction by way of a jump member by a guide member biased toward a glass sheet surface.
Japanese Patent application Laid-Open (Kokai) No. 61-139920 proposes an apparatus in which, to maintain a fixed distance between a stationary original glass stand and an optical system moving in a sub-scanning direction, a roller protrudes from the optical system toward the back surface of the original glass stand and a biasing effect is provided, thereby maintaining a fixed focal distance in conformity with the configuration of the original glass stand.
Japanese Patent application Laid-Open (Kokai) No. 10-186535 discloses an apparatus in which, as shown in FIG. 8, a stationary original D on a first glass sheet 12 is read while moving a CIS 1 as image reading means in the sub-scanning direction and in which, on a second glass sheet 13, the CIS 1 remains stationary and reads a moving original S.
In the above-mentioned invention, however, when the maximum-size original D is read on the first glass sheet 12, the CIS 1, after leaving the trailing end E of the original, undergoes speed reduction and advances by a distance F of approximately 10 mm before it stops.
In the above-mentioned conventional techniques, the sheet scanner portion which reads the original S while moving the original and the flat bed scanner portion which reads the original D arranged on the original glass stand, are respectively secured to the main body, so that, to form an image reading apparatus using a contact-type image sensor (CIS) of a shallow focal depth, the following problems are involved.
In the construction proposed in Japanese Patent Publication No. 3-37348, the optical system is scanned in accordance with the structure of the main body, and the glass sheet of the sheet scanner portion and the glass sheet of the flat bed scanner portion are separated and respectively fixed in position.
Thus, in an apparatus utilizing a CIS, it is necessary to set the heights of the two glass sheets with high accuracy to guide the original within the focal depth of the CIS. Furthermore, taking into account the construction from the sensor to the glass sheets and the number of parts, it is difficult to ensure an accuracy which meets a desired level. To ensure such accuracy, it is necessary to perform height adjustment on the glass sheets or the optical system in the assembly step.
Further, since the ADF portion is secured to the apparatus main body in a state in which the ADF portion is separated from the pressure plate, the original supply portion is arranged outside the pressure plate, so that the size of the entire main body is rather large as compared with an apparatus in which the original supply portion is provided on the pressure plate.
In the case of the proposal made in Japanese Patent application Laid-Open No. 63-138863, there is provided a jump stand 4 (FIG. 8) for picking up an original that has undergone a U-turn and has been read. When the glass sheet on the sheet scanner side and the glass sheet on the flat bed scanner side are integrated, it is necessary, in order to pick up the original by the jump stand 4, to arrange the side of the jump stand 4 which first comes into contact with the original (the upstream side with respect to the original conveying direction) lower than the glass sheet surface. Otherwise, original jamming will be caused by the edge of the jump stand 4.
On the other hand, when the upstream side of the jump stand 4 is arranged lower than the glass sheet surface, it is necessary to provide a groove in the glass sheet surface.
Provision of a groove in the glass sheet leads to a substantial increase in cost. Further, it also involves an extreme deterioration in the strength of the portion where the groove is provided.
Unlike the apparatus as disclosed in Japanese Patent application Laid-Open No. 63-138863, in which the glass sheet of the sheet scanner portion and the glass sheet of the flat bed scanner portion are integrated, a construction in which the glasses are separated as in the case of the proposal made in Japanese Patent Application Laid-Open No. 61-49920 has a problem in that the focal distance is small and, in an apparatus using a CIS in which the distance to the back surface of the glass sheet is approximately 1 mm, the glass sheet support portion and a step portion between the glass sheets are in the way, making it difficult to move the CIS between the sheet scanner portion and the flat bed scanner portion.
In the case of the proposal made in the Japanese Patent application Laid-Open No. 10-186535, the CIS 1 moves while making a vertical movement between the first glass sheet 12 and the second glass sheet 13, and the problem of the movement between the two glass sheets is solved up to a point. However, it is necessary to cause the CIS to move by a great distance in the sub-scanning direction.
FIG. 8 shows a second embodiment of the above-mentioned conventional technique, in which the support portion between the glass sheets 12 and 13 is formed by a step of 0.5 mm having a slope, and the CIS 1 held in contact with the glass sheets by a roller is moved. In the case of a glass sheet of a large size, such as an A-3 size, a problem in terms of strength is involved when supporting the glass sheet with a step of 0.5 mm.
FIG. 9 shows a third embodiment of Japanese Patent application Laid-Open No. 10-186535, in which the support portion between the glass sheets 12, 13 is flush with the glass sheet surfaces only in the portion in which the CIS 1 moves while being in contact with the glass sheets 12, 13. In this construction, the glass sheet edge portion may collide with the contact member 2 of the CIS 1, in which case the contact member 2 is worn, resulting in a change in the focal distance of the CIS 1.
Apart from this, although not explicitly proposed as an invention, in the conventional construction of FIG. 8 there is provided a speed reduction range F of approximately 10 mm to the right of the right-hand end E of the original D, and, further on the outside thereof, there exists an extra portion G of approximately 7 mm at which the frame 3 supports the end portion of the first glass sheet 12.
Further, to the left of the second glass sheet 13, there exists a portion H (having a length of approximately 5 mm) supported by the frame 3, with the result that the apparatus is rather long.
In the apparatus shown in FIG. 9, in which the distance between the first glass sheet 12 and the second glass sheet 13 is large, there is the possibility of the CIS 1 being thrust into the gap therebetween in an inclined state.